1. Field of the Invention
The present invention relates to a polymer composition based on titanium oxide, to its use as a semiconductor element in a photovoltaic cell, and to a method for preparing it.
2. Description of the Related Art
Photovoltaic cells convert solar energy into electricity by exploiting the photovoltaic effect that exists at the interface of a p-n junction between two semiconductors. Semiconductors based on silicon have been used, but the high cost of the raw material is not favorable to the industrial development of such cells. Silicon has therefore been replaced with titanium oxide TiO2 which is an inexpensive semiconductor and has stable photocatalytic properties. Its applications in the photovoltaic field are, however, limited, as it absorbs only within a narrow range of the solar spectrum, owing to a wide bandgap. This range corresponds to the UV part and covers less than 10% of the entire solar spectrum. One solution consists in covering the surface of the titanium oxide with a photosensitizer in order to extend its photoactivity range into the region of the solar spectrum. This technique has been employed using a ruthenium polypyridinic complex as photosensitizer (U.S. Pat. No. 5,084,365) and it has allowed efficiencies of around 12% to be achieved. The cells containing, as semiconductor, titanium oxide activated by a photosensitizer have a production cost less than that of the photovoltaic cells of the prior art. However, their operating lifetime, which is about 10 years, is considerably shorter than that of single-crystal silicon cells (which is around 20 years), and their efficiency is lower.